Dual view displays have been known for many years as an eye-catching means for attracting a viewer's attention. In general, dual view displays are formed by providing a mounting surface formed by a series of rectangular planar surfaces of substantially equal size which are connected side-by-side. The planar surfaces are situated in a "zig-zag" or accordion-folded relation wherein each planar surface is situated parallel to one of two viewing planes, these two viewing planes being situated generally perpendicular to each other, and wherein each planar surface is parallel to a different viewing plane than the planar surfaces adjacent to it. A first image is then applied to the planar surfaces which are parallel to one viewing plane, and a second image is applied to the planar surfaces parallel to the other viewing plane. The images are applied as if each set of parallel planar surfaces was not interrupted by the other set, that is, where two parallel planar surfaces are separated by an intermediate (and perpendicular) planar surface, the image is neatly divided between the two parallel planar surfaces as if the intermediate planar surface was not present. As a result, if a viewer views the dual view display from a line of sight which is normal to the first viewing plane, the first image borne on the planar surfaces parallel to the first viewing plane appears as a coherent and substantially continuous image, and the second image is not visible. If a viewer instead views the dual view display from a line of sight which is normal to the second viewing plane, the second image borne on the planar surfaces parallel to the second viewing plane appears as a coherent and substantially continuous image, and the first image is not visible. If a viewer views the dual view display from intermediate lines of sight, sections of both images are visible, but they are commingled or "interleaved" and do not form a coherent image.
An example of a dual view display of this type is given in U.S. Pat. No. 4,937,960 to Otake. Otake illustrates a rotating three-sided display unit, each side of which constitutes an accordion-folded mounting surface bearing a dual view display. Because the three-sided unit is rotatable, one may turn the unit to see two adjacent sides of the display unit at once and thus view an image on each of these two sides. If the unit is instead rotated so that a single side of the display unit is oriented approximately normal to the viewer's line of sight, the viewer will see only the non-coherent image produced by the interleaved image sections borne on this side. Different embodiments of the display unit are illustrated in FIGS. 1 and 4 of Otake, wherein sectioned images (see FIG. 3) are interleaved and each image section is directly attached to the accordion-folded mounting surfaces; FIG. 5, wherein interleaved image sections are joined as shown in FIGS. 6, 11, and 12, accordion-folded, and then directly attached to the accordion-folded mounting surfaces; and FIG. 9, wherein an accordion-folded transparent cover is provided spaced from a planar backing wall so that the aforementioned attached image sections of FIGS. 6, 11, and 12 may be accordion-folded and fit between the cover and backing wall. FIGS. 10 and 13 also illustrate single-sided display units wherein the accordion-folded attached image sections of FIGS. 6, 11, and 12 may be fit and wherein no accordion-folded mounting surface is provided, but wherein flanges nevertheless hold the attached image sections in an accordion-folded shape. The Otake embodiments which illustrate direct fixation of image sections to an accordion-folded mounting surface have the advantage that they will always firmly maintain the image sections at the desired viewing angle, but they have the disadvantage that they do not allow removal and replacement of the image sections. In contrast, the embodiments of FIGS. 9, 10, and 13 allow removal and replacement of image sections, but the lack of support of the image sections (i.e., the lack of any means for firmly maintaining the entire areas of the image sections against the accordion-folded surfaces) gives rise to the possibility of distortion if the image sections deviate from a precisely planar configuration.
Dual view displays are eye-catching and relatively inexpensive to produce in terms of material costs. However, they have not gained widespread use owing to difficulties encountered during their production. The problem is mainly that of properly sectioning, interleaving, and mounting the dual images on the accordion-folded mounting surface: unless the two images are properly sectioned and the sections are precisely registered on the planar sections corresponding to their respective viewing planes the images will suffer from distortion or an unnatural appearance. If the image sections are cut too small to precisely fit their planar sections, their image will be interrupted by gaps when viewed at a normal; if the sections are cut too large, their image will appear to be missing vertical strips. Further distortion can appear if the vertical edges (horizontal borders) are not cut precisely straight, and/or if any sections are mounted to the mounting surface with a slight offset in a horizontal, vertical, or other directions (i.e., if they are not precisely registered prior to attachment). Quite simply, an error in producing a single section can "break" and ruin the entire image, and since each image is generally divided into numerous sections prior to interleaving and joining the images, the risk of error is high. At FIGS. 14 and 15 and column 6 line 14 onward of Otake, a method of accurately and automatically sectioning, interleaving, and attaching the image sections of FIGS. 6, 11, and 12 is illustrated and described, but this method requires specialized production equipment and is not feasible for the common user.
One solution proposed for the problems of sectioning, interleaving, and registering images is presented in U.S. Pat. No. 3,406,476 to Wilcox. Wilcox describes providing a series of elongated triangular prisms (i.e., beams or tubes having cross-sections shaped like equilateral triangles) which combine to provide an accordion-folded surface when situated side-by-side in parallel relation. The triangular prisms are set side by side within a receiving template so that each has one side situated adjacent to and in the same plane as one side on the other prisms. A continuous planar surface is thus formed. An image-bearing picture may then be glued or otherwise mounted on this surface. The picture may then be cut at the edge of each prism to section the image, thus leaving an image section adhered to each prism. The prisms are then lifted, rotated 120.degree. so that each prism presents a new side (thereby forming another planar surface to which a picture may be affixed), and replaced in the receiving template. Another picture is then mounted to this planar surface and sectioned. The prisms may then be mounted in parallel abutting relation (using the leftover unadorned sides of the prisms as the mounting surface) so that the image sections borne thereon are displayed in adjacent interleaved fashion to provide a dual view display.
While the method and apparatus of Wilcox provides a useful development, it is labor-intensive and difficult to practice. Initially, the cut-and-glue procedure used for sectioning, interleaving, and attaching image sections is time-consuming if a user wishes to obtain the precision necessary to avoid registration problems. Once an image is affixed to the surfaces of multiple prisms, the boundaries between these prisms are obscured, making it difficult for a user to know where to cut to section the images and separate the prisms. If an imprecise cut is made during sectioning, the view of the image sections can be distorted.
Another solution proposed for the problems of sectioning, interleaving, and registration is presented in U.S. Pat. No. 4,233,767 to Hryhorczuk. Hryhorczuk provides a kit including an accordion-folded mounting surface and two template sheets having opposing adhesive-coated faces. The opposing adhesive faces of each template sheet are provided with a protective backing which may be peeled away to reveal the adhesive, and the backing covering one of the adhesive faces is provided with printed lines. These lines divide the backing into an array of planar sections corresponding in size and shape to the planar sections of the accordion-folded mounting surface. The user may take two pictures, peel away the non-lined backing on each template sheet to reveal an adhesive face, and adhere this exposed adhesive face to the rear of a respective picture. The rear of each picture then displays the lined backing of its adhered template sheet. The pictures may then be cut along the printed lines of the backing, thereby sectioning the pictures into image sections sized to fit upon the planar sections of the accordion-folded mounting surface. The lined backing on each of the image sections may then be peeled away, thus providing each image section with an adhesive rear face so that the image sections can be easily adhered to the accordion-folded mounting surface. After being properly interleaved, the image sections are adhered to the accordion-folded mounting surface to complete the dual view display. As with Wilcox, unless the two images are properly sectioned, interleaved, and mounted to the planar sections corresponding to their respective viewing planes, and unless the image sections are mounted with proper registration, the images will suffer from distortion or an unnatural appearance.
The aforementioned drawbacks are not significant if one does not require a "perfect" dual view display, allowing use of less expensive manufacturing measures. As an example, U.S. Pat. No. 4,422,253 to Babberl illustrates a dual view display wherein joined image sections (such as that of FIGS. 6, 11, and 12 of Otake) are accordion-folded and placed in a box which maintains the image sections in a generally accordion-folded shape. Creation of the sheet of joined image sections is subject to the same difficulties as those encountered with Wilcox and Hryhorczuk. However, an additional problem is introduced in that the joined image sections are unsupported by an accordion-folded mounting surface, and thus the image sections are not maintained at precise angles. As a result, the images will suffer from distortion.
The ultimate object of a high-quality dual view display is to have each of its images appear as a continuous two-dimensional image when the image is viewed from a line normal to its viewing plane--in other words, the image should appear to be a standard image mounted on a standard two-dimensional surface. The dual view display will thus appear to viewers to be an ordinary two-dimensional display, but will then create a startling effect when viewers move to a different viewing angle, at which point it will become apparent that more than one image is present. Dual view displays appear deceptively simple to make, but when it is considered that even minor errors in sectioning, interleaving, and registration can significantly degrade image quality, it should be apparent that the additional time and labor needed for precise construction makes dual view displays prohibitively expensive.